5 - 108 ANTI-LOCK 6 BRAKE SYSTEM

The self diagnostic ABS startup cycle begins when the ignition switch is in the on position. An electrical check is completed on the ABS components such as Wheel Speed Sensor Continuity and System and other Relay continuity. During this check the Amber Anti-Lock Light is on for approximately 1-2 seconds.

Further Functional testing is accomplished once the vehicle is set in motion.

(1)The solenoid valves and the pump/motor are activated briefly to verify function.

(2)The voltage output from the wheel speed sensors is verified to be within the correct operating range.

If the vehicle is not set in motion within 3 minutes from the time the ignition switch is set in the on position. The solenoid test is bypassed but the pump/motor is activated briefly to verify that it is operating correctly.

WARNING SYSTEMS OPERATION

The ABS system uses an Amber Anti-Lock Warning Lamp, located in the instrument cluster. The purpose of the warning lamp is discussed in detail below.

The Amber Anti-Lock Warning Light will turn on when the (CAB) detects a condition which results in a shutdown of the Anti-Lock function. The Amber AntiLock Warning Lamp is normally on until the (CAB) completes its self tests and turns the lamp off (approximately 1-2 seconds). When the Amber Anti-Lock Warning Light is on only the Anti-Lock function of the brake system if affected. The standard brake system and the ability to stop the car will not be affected when only the Amber Anti-Lock Warning Light is on.

NORMAL OPERATION OF WARNING LAMP

With the ignition in the Crank position, the Red Brake Warning Lamp will turn on as a bulb check. The Amber Anti-Lock Warning Lamp will stay on for 1-2 seconds then turn off. Once verification of the self diagnosis is completed.

ANTI-LOCK BRAKE SYSTEM COMPONENTS

The following is a detailed description of the AntiLock Brake System components. For information on servicing the Four Wheel Disk Brake System, see the standard Brake section of this Service Manual.

MODULATOR ASSEMBLY

WARNING: THE ONLY PART OF THE MODULATOR ASSEMBLY THAT IS A SERVICEABLE COMPONENT IS THE DELTA P SWITCH. THE REMAINING COMPONENTS OF THE MODULATOR ASSEMBLY ARE NOT SERVICEABLE ITEMS AND NO ATTEMPT IN ANY WAY SHOULD BE MADE TO REMOVE OR SERVICE ANY OTHER PARTS OF THE MODULATOR ASSEMBLY.

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The Modulator Assembly (Fig. 1) is located under the battery tray and is covered with an acid shield. The Modulator Assembly contains the following components for controlling the Anti-Lock braking system. 2 Isolation Valves, 4 Build/Decay Valves, 4 Shuttle Orifices, 2 Fluid Sumps, 2 Accumulators, a Pump/Motor and a Pressure Differential Valve/ Switch. Also attached to the Modulator Assembly are 4 brake tubes which are connected to an 8 way connector block. The connector block is mounted to the left frame rail below the master cylinder in the same location as the non ABS equipped combination valve. The wheel brake lines are attached to the system via the connector block.

ISOLATION VALVES

The Isolation Valves are used to isolate the master cylinder from the rest of the brake hydraulic circuit during an Anti-Lock stop. Two Isolation Valves are used, one for the primary circuit and one for the secondary circuit. The Isolation Valves are spring loaded in the released position. In the released position the Isolation Valves provide a fluid path from the master cylinder outputs to the wheel brakes via the Build/Decay valves. When actuated it provides a fluid path from the accumulator (which was charged by the Pump/Motor during ABS operation) to the Build/Decay valves through the Shuttle Orifices.

BUILD/DECAY VALVES

There are 4 Build/Decay valves, one for each wheel. In the released position they provide a fluid path from the wheel brakes to the Isolation Valve through the shuttle orifices. In the actuated (decay) position, they provide a fluid path from the wheel brakes to the sump. The Build/Decay valves are spring loaded in the released (build) position.

SHUTTLE ORIFICE

There are 4 Shuttle Orifice Valves, one for each wheel. The Shuttle Orifice Valve is a hydraulically actuated valve which shuttles when the Build/Decay valve is actuated. Actuating of the Build/Decay valve causes a pressure differential to be created across the Shuttle Orifice Valve. This acts like placing an orifice (restriction) in the line between the Isolation Valve and the Build/Decay Valve. This restriction provides a controlled build rate to each wheel brake during an Anti-Lock stop. The Shuttle Orifice Valve will remain in the orificed position until the ABS cycle is complete. When the ABS cycle has been completed the Isolation and Build/Decay valves will return to their released position which will equalize the pressure across the Shuttle Orifice Valves. When

the pressure equalizes, the spring loaded Shuttle Orifice valves will return to the unrestricted position.

FLUID SUMPS

There are two Fluid Sumps in the Hydraulic Assembly, one each for the primary and secondary hydraulic circuits. The Fluid Sumps store the brake fluid that is decayed from the wheel brakes during ABS cycle. This fluid is then pumped to an accumulator and/or the hydraulic system in order to provide build pressure. The typical pressure in the sumps is 50 psi, During ABS operation only.

HYDRAULIC SPRING ACCUMULATOR

The Hydraulic Spring Accumulators (Fig. 2) (one on each circuit) are used to store pressurized hydraulic brake fluid during ABS operation only. This fluid is used during hard braking when the ABS system is activated, to supplement brake pressure when required. During normal Non ABS braking operation there is NO pressurized brake fluid stored in the accumulators. The Hydraulic Spring Accumulators are not a serviceable part of the Modulator Assembly and should never be removed from the assembly.

PRESSURE DIFFERENTIAL VALVE/SWITCH (DELTA P SWITCH)

The Pressure Differential Valve/Switch is located inside the hydraulic assembly. This valve/switch functions the same as the Pressure Differential Valve/Switch located in the combination valve on standard brake systems. The delta P switch monitors the primary and secondary hydraulic circuits for a difference in pressure. A pressure difference greater than 225 psi. Will move and latch the shuttle to

Fig. 2 Hydraulic Spring Accumulator

ground the Red Brake Warning Light circuit. This will in turn, turn on the Red Brake Warning Light in the instrument panel to warn the driver of a hydraulic system problem. This Pressure Differential Valve Switch is a replaceable item of the Modulator Assembly. The Red Brake Warning Light indicates a problem with the foundation brake system and not the Anti-Lock system.

5 - 110 ANTI-LOCK 6 BRAKE SYSTEM

PUMP/MOTOR ASSEMBLY

The Modulator Assembly contains 2 Pump Assemblies, one each for the primary and secondary hydraulic circuits. Both pumps are driven by a common electric motor which is part of the Modulator Assembly. The pumps pick up fluid from the sumps to supply pressure to the accumulators or hydraulic system via the isolation valves during an Anti-Lock stop. The motor only runs during an ABS stop and is controlled by the (CAB) via the Pump/Motor Relay. The Pump/Motor Assembly is not a serviceable item. If it requires service the Modulator Assembly must be replaced.

PROPORTIONING VALVES

Two Proportioning Valves (Fig. 3) are used in the system, one for each rear brake hydraulic circuit. The Proportioning Valves function the same as in a standard brake system. The Proportioning Valves are located on the bottom of the hydraulic assembly (Fig. 1). They are the same screw in type as the ones used on the Bendix Anti-Lock 10 and Bosh Anti-Lock Brake systems.

Fig. 3 Proportioning Valve Identification

WHEEL SPEED SENSORS

One Wheel Speed Sensor (WSS), is located at each wheel (Figs. 4 and 5), and sends a small (AC) signal to the control module (CAB). This signal is generated by magnetic induction. The magnetic induction is cre-

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ated, when a toothed sensor ring Tone Wheel (Fig. 6) passes a stationary magnetic Wheel Speed Sensor. The (CAB) converts the (AC) signal generated at each wheel into a digital signal. If a wheel locking tendency is detected, the (CAB) will then modulate hydraulic pressure to prevent the wheel(s) from locking.

Fig. 4 Front Wheel Speed Sensor

Fig. 5 Rear Wheel Speed Sensor

The front Wheel Speed Sensor is attached to a boss in the steering knuckle (Fig. 4). The tone wheel is part of the outboard constant velocity joint. The rear Wheel Speed Sensor is mounted to the caliper adaptor (Fig. 5) and the rear tone wheel is an integral part of the rear wheel hub (Fig. 6). The speed sensor air gap is NOT adjustable.

Fig. 6 Tone Wheel (Typical)

The four Wheel Speed Sensors are serviced individually. The front Tone Wheels are serviced as an assembly with the outboard constant velocity joint. The rear Tone Wheels are serviced as an assembly with the rear brake hub.

Correct Anti-Lock system operation is dependent on the vehicle's wheel speed signals, that are generated by the Wheel Speed Sensors. The vehicle's wheels and tires must all be the same size and type to generate accurate signals. In addition, the tires must be inflated to the recommended pressures for optimum system operation. Variations in wheel and tire size or significant variations in inflation pressure can produce inaccurate wheel speed signals.

CONTROLLER ANTI-LOCK BRAKE (CAB)

The Anti-Lock Brake Controller is a small microprocessor based device which monitors the brake system and controls the system while it functions in AntiLock mode. The CAB is mounted on the top of the right front frame rail and uses a 60-way system connector (Fig. 7). The power source for the CAB is through the ignition switch in the Run or On position.

THE CONTROLLER ANTI-LOCK BRAKE (CAB) IS NOT ON THE CCD BUS

The primary functions of the (CAB) are:

(1)Detect wheel locking tendencies.

(2)Control fluid modulation to the brakes while in Anti-Lock mode.

(3)Monitor the system for proper operation.

(4)Provide communication to the DRB II while in diagnostic mode.

The (CAB) continuously monitors the speed of each wheel, through the signals generated at the Wheel Speed Sensors, to determine if any wheel is beginning

Fig. 7 Location Controller Anti-Lock Brake (CAB)

to lock. When a front wheel locking tendency is detected, the (CAB) will isolate the master cylinder from the wheel brakes. This is done by activating the Isolation Valves. The (CAB) then commands the appropriate Build/Decay valves to modulate brake fluid pressure in some or all of the hydraulic circuits. The (CAB) continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.

The (ABS) system is constantly monitored by the (CAB) for proper operation. If the (CAB) detects a fault, it will turn on the Amber Anti-Lock Warning Lamp and disable the ABS braking system. The normal Non ABS braking system will remain operational.

The (CAB) contains a self-diagnostic program which will turn on the Amber Anti-Lock Warning Lamp when a system fault is detected. Faults are stored in a diagnostic program memory. There are 16 fault codes which may be stored in the (CAB) and displayed through the DRB II. These fault codes will remain in the (CAB) memory even after the ignition has been turned off. The fault codes can be cleared by using the DRB II diagnostics tester, or they will be automatically cleared from the memory after (50) ignition switch on/off cycles.

CONTROLLER ANTI-LOCK BRAKE (INPUTS)

²Four wheel speed sensors.

²Stop lamp switch.

²Ignition switch.